Resist composition and method of forming resist pattern

ABSTRACT

A resist composition including a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, the acid-generator component (B) including at least one acid generator (B1) represented by general formula (b1) shown below, at least one acid generator (B2) represented by general formula (b2) shown below, and at least one acid generator (B3) represented by general formula (b3) shown below (wherein IV to R 3  each independently represents a cyclic group which may have a substituent, a chain alkyl group, or a chain alkenyl group; Y 1  represents a single bond or a divalent linking group containing an oxygen atom; M 1   +  to M 3   +  represents a monovalent organic cation; n represents an integer of 1 to 4; m represents an integer of 0 to 4; provided that, when m is 0, the carbon atom adjacent to the sulfur atom within R 2  has no fluorine atom bonded thereto). 
       R 1 —Y 1 —(CF 2 ) n —SO 3   − M 1   +   (b1)
 
       R 2 —(CH 2 ) m —SO 3   − M 2   +   (b2)
 
       R 3 —COO − M 3   +   (b3)

TECHNICAL FIELD

The present invention relates to a resist composition and a method of forming a resist pattern.

Priority is claimed on Korean Patent Application No. 2015-0144911, filed Oct. 16, 2015, the content of which is incorporated herein by reference.

DESCRIPTION OF RELATED ART

In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.

A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.

In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.

Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam, extreme ultraviolet radiation (EUV), and X ray.

In recent years, due to prolonging of ArF lithography, demands are becoming more strict when conducting lithography in terms of reducing roughness and reducing fluctuation of hole size (CD). A method is known in which an photoacid generator having a free anion with relatively weak acidity is used as an acid diffusion control agent (quencher), so as to improve dissolution contrast between exposed portions and unexposed portions (Patent Literature 1).

DOCUMENTS OF RELATED ART Patent Literature

-   [Patent Literature 1] Japanese Unexamined Patent Application, First     Publication No. 2009-244352

SUMMARY OF THE INVENTION

However, as the pattern becomes finer, the light diffraction is reaching a limit, the contrast of light is deteriorated. As a result, in the case of a conventional resist composition, when a pattern is formed with a weak contrast of light, acid is generated more than necessary, thereby becoming a source of roughness.

The present invention takes the above circumstances into consideration, and the present inventors have newly found that, in order to suppress the above phenomenon, addition of a photoacid generator having a medium acid strength is effective in functioning for both acid generation and acid diffusion control.

Such effect can be achieved by virtue of including, at the same time, a photoacid generator having a fluoroalkylsulfonic acid which is an extremely strong acid as an anion, a photoacid generator having a sulfonic acid which is a strong acid as an anion, and a photoacid generator having a carboxylic acid which is a weak acid as an anion. An object of the present invention is to provide a resist composition exhibiting excellent lithography properties by virtue of including such photoacid generators, and a method of forming a resist pattern by using the resist composition.

For achieving the above object, the present invention employs the following configuration.

A first aspect of the present invention is a resist composition including a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, the acid-generator component (B) including at least one acid generator (B1) represented by general formula (b1) shown below, at least one acid generator (B2) represented by general formula (b2) shown below, and at least one acid generator (B3) represented by general formula (b3) shown below.

[Chemical Formula 1]

R¹—Y¹—(CF₂)_(n)—SO₃ ⁻M₁ ⁺  (b1)

R²—(CH₂)_(m)—SO₃ ⁻M₂ ⁺  (b2)

R³—COO⁻M₃ ⁺  (b3)

In the formulae, R¹ to R³ each independently represents a cyclic group which may have a substituent, a chain alkyl group, or a chain alkenyl group; Y¹ represents a single bond or a divalent linking group containing an oxygen atom; M₁ ⁺ to M₃ ⁺ represents a monovalent organic cation; n represents an integer of 1 to 4; m represents an integer of 0 to 4; provided that, when m is 0, the carbon atom adjacent to the sulfur atom within R² has no fluorine atom bonded thereto.

A second aspect of the present invention is a method of forming a resist pattern, including: using a resist composition according to the first aspect to form a resist film on a substrate, exposing the resist film, and developing the resist film to form a resist pattern.

According to the present invention, there are provided a resist composition which exhibits excellent lithography properties, and a method of forming a resist pattern using the resist composition.

DETAILED DESCRIPTION OF THE INVENTION

In the present description and claims, the term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity.

The term “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified.

The term “alkylene group” includes linear, branched or cyclic, divalent saturated hydrocarbon, unless otherwise specified. The same applies for the alkyl group within an alkoxy group.

A “halogenated alkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group is substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

A “fluorinated alkyl group” or a “fluorinated alkylene group” is a group in which part or all of the hydrogen atoms of an alkyl group or an alkylene group have been substituted with a fluorine atom.

The term “structural unit” refers to a monomer unit that contributes to the formation of a polymeric compound (resin, polymer, copolymer).

A “structural unit derived from an acrylate ester” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of an acrylate ester.

An “acrylate ester” refers to a compound in which the terminal hydrogen atom of the carboxy group of acrylic acid (CH₂═CH—COOH) has been substituted with an organic group.

The acrylate ester may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. The substituent (R^(α)) with which the hydrogen atom bonded to the carbon atom at the α-position is substituted is an atom other than the hydrogen atom or a group, and examples thereof include an alkyl group having from 1 to 5 carbon atoms, a halogenated alkyl group having from 1 to 5 carbon atoms, and a hydroxyalkyl group. A carbon atom on the α-position of an acrylate ester refers to the carbon atom bonded to the carbonyl group, unless specified otherwise.

Hereafter, an acrylate ester having the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is sometimes referred to as “α-substituted acrylate ester”. Further, acrylate esters and α-substituted acrylate esters are collectively referred to as “(α-substituted) acrylate ester”.

A “structural unit derived from a hydroxystyrene derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of hydroxystyrene or a hydroxystyrene derivative.

The term “hydroxystyrene derivative” includes compounds in which the hydrogen atom at the α-position of hydroxystyrene has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof. Examples of the derivatives thereof include hydroxystyrene in which the hydrogen atom of the hydroxy group has been substituted with an organic group and may have the hydrogen atom on the α-position substituted with a substituent; and hydroxystyrene which has a substituent other than a hydroxy group bonded to the benzene ring and may have the hydrogen atom on the α-position substituted with a substituent. Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

As the substituent which substitutes the hydrogen atom on the α-position of hydroxystyrene, the same substituents as those described above for the substituent on the α-position of the aforementioned α-substituted acrylate ester can be mentioned.

A “structural unit derived from vinylbenzoic acid or a vinylbenzoic acid derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of vinylbenzoic acid or a vinylbenzoic acid derivative.

The term “vinylbenzoic acid derivative” includes compounds in which the hydrogen atom at the α-position of vinylbenzoic acid has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof. Examples of the derivatives thereof include benzoic acid in which the hydrogen atom of the carboxy group has been substituted with an organic group and may have the hydrogen atom on the α-position substituted with a substituent; and benzoic acid which has a substituent other than a hydroxy group and a carboxy group bonded to the benzene ring and may have the hydrogen atom on the α-position substituted with a substituent. Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

A “styrene derivative” refers to a compound in which the hydrogen atom on the α-position of styrene is substituted with a substituent such as an alkyl group, a halogenated alkyl group or the like.

A “structural unit derived from styrene” or “structural unit derived from a styrene derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of styrene or a styrene derivative.

As the alkyl group as a substituent on the α-position, a linear or branched alkyl group is preferable, and specific examples include alkyl groups of 1 to 5 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

Specific examples of the halogenated alkyl group as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group as the substituent on the α-position” are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

Specific examples of the hydroxyalkyl group as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group as the substituent on the α-position” are substituted with a hydroxy group. The number of hydroxy groups within the hydroxyalkyl group is preferably 1 to 5, and most preferably 1.

The expression “may have a substituent” means that a case where a hydrogen atom (—H) is substituted with a monovalent group, or a case where a methylene group (—CH₂—) is substituted with a divalent group.

The term “exposure” is used as a general concept that includes irradiation with any form of radiation.

<<Resist Composition>>

A first aspect of the present invention is a resist composition which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, the resist composition including a base component (A) which exhibits changed solubility in an alkali developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, the acid-generator component (B) including at least one acid generator represented by the aforementioned general formula (b1), at least one acid generator represented by the aforementioned general formula (b2) shown below, and at least one acid generator represented by the aforementioned general formula (b3).

In the present embodiment, the resist composition contains a base component (A) (hereafter, referred to as “base component (A)”) which exhibits changed solubility in a developing solution.

When a resist film is formed using the resist composition and the formed resist film is subjected to a selective exposure, acid is generated at exposed portions, and the generated acid acts on the component (A) to change the solubility of the component (A) in a developing solution, whereas the solubility of the component (A) in a developing solution is not changed at unexposed portions, thereby generating difference in solubility in a developing solution between exposed portions and unexposed portions. Therefore, by subjecting the resist film to development, the exposed portions are dissolved and removed to form a positive-tone resist pattern in the case of a positive resist, whereas the unexposed portions are dissolved and removed to form a negative-tone resist pattern in the case of a negative resist.

In the present specification, a resist composition which forms a positive resist pattern by dissolving and removing the exposed portions is called a positive resist composition, and a resist composition which forms a negative resist pattern by dissolving and removing the unexposed portions is called a negative resist composition.

In the present embodiment, the resist composition may be either a positive resist composition or a negative resist composition. Further, the resist composition of the present invention may be used in a dual tone developing process.

Further, in the present embodiment, the resist composition may be applied to an alkali developing process using an alkali developing solution in the developing treatment, or a solvent developing process using a developing solution containing an organic solvent (organic developing solution) in the developing treatment, and preferably a solvent developing process.

The resist composition usable in forming a resist pattern has a function of generating acid upon exposure The resist composition contains an acid-generator component (B), and the component (A) may be capable of generating acid upon exposure.

In the case where the component (A) generates acid upon exposure, the component (A) is a “base component which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid”. In the case where the component (A) is a base component which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, the component (A1) described later is preferably a polymeric compound which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid. As the polymeric compound, a resin having a structural unit which generates acid upon exposure can be used. As the structural unit which generates acid upon exposure, a conventional structural unit can be used.

<Component (A)>

In the present invention, the term “base component” refers to an organic compound capable of forming a film, and is preferably an organic compound having a molecular weight of 500 or more. When the organic compound has a molecular weight of 500 or more, the film-forming ability is improved, and a photosensitive resin pattern of nano level can be easily formed.

The organic compound used as the base component is broadly classified into non-polymers and polymers.

In general, as a non-polymer, any of those which have a molecular weight in the range of 500 to less than 4,000 is used. Hereafter, a “low molecular weight compound” refers to a non-polymer having a molecular weight in the range of 500 to less than 4,000.

As a polymer, any of those which have a molecular weight of 1,000 or more is generally used. Hereafter, a “resin” refers to a polymer having a molecular weight of 1,000 or more.

As the molecular weight of the polymer, the weight average molecular weight in terms of the polystyrene equivalent value determined by gel permeation chromatography (GPC) is used.

As the component (A′), a resin, a low molecular weight compound, or a combination thereof may be used.

The component (A) is a base component which exhibits increased solubility in a developing solution under action of acid.

In the present invention, the component (A) may be a component that generates acid upon exposure.

In the present embodiment, the component (A) preferably contains a polymeric compound (A1) having a structural unit containing an acid decomposable group which exhibits increased polarity by the action of acid (hereafter, referred to as “structural unit (a1)”), a structural unit derived from an acrylate ester containing an —SO₂— containing cyclic group, a lactone-containing cyclic group, a carbonate-containing cyclic group or any other heterocyclic group (hereafter, referred to as “structural unit (a2)”), and a structural unit containing a polar group-containing aliphatic hydrocarbon group (hereafter, referred to as “structural unit (a3)”).

(Structural Unit (a1))

The structural unit (a1) is a structural unit containing an acid decomposable group that exhibits increased polarity by the action of acid.

The term “acid decomposable group” refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of an acid.

Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfo group (—SO₃H). Among these, a sulfo group or a polar group containing —OH in the structure thereof (hereafter, referred to as “OH-containing polar group”) is preferable, a carboxy group or a hydroxy group is more preferable, and a carboxy group is particularly desirable.

More specifically, as an example of an acid decomposable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been protected with an acid dissociable group) can be given.

Here, the “acid dissociable group” includes:

(i) a group in which the bond between the acid dissociable group and the adjacent atom is cleaved by the action of acid; and

(ii) a group in which one of the bonds is cleaved by the action of acid, and then a decarboxylation reaction occurs, thereby cleaving the bond between the acid dis sociable group and the adjacent atom.

It is necessary that the acid dissociable group that constitutes the acid decomposable group is a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. As a result, the polarity of the entire component (A1) is increased. By the increase in the polarity, the solubility in an alkali developing solution changes and, the solubility in an organic developing solution is relatively decreased.

The acid dissociable group is not particularly limited, and any of the groups that have been conventionally proposed as acid dissociable groups for the base resins of chemically amplified resists can be used.

Examples of the acid dissociable group for protecting the carboxy group or hydroxy group as a polar group include the acid dissociable group represented by general formula (a1-r-1) shown below (hereafter, for the sake of convenience, sometimes referred to as “acetal-type acid dissociable group”).

In the formula, Ra′¹ and Ra′² represents a hydrogen atom or an alkyl group; and Ra′³ represents a hydrocarbon group, provided that Ra′³ may be bonded to Ra′¹ or Ra′²; and * represents a valence bond.

In formula (a1-r-1), as the lower alkyl group for Ra′¹ and Ra′², the same lower alkyl groups as those described above the alkyl groups as the substituent which may be bonded to the carbon atom on the α-position of the aforementioned α-substituted alkylester can be used, although a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

The hydrocarbon group for Ra′³ is preferably an alkyl group of 1 to 20 carbon atoms, more preferably an alkyl group of 1 to 10 carbon atoms, and still more preferably a linear or branched alkyl group. Specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a 1,1-dimethylethyl group, a 1,1-diethylpropyl group, a 2,2-dimethylpropyl group and a 2,2-dimethylbutyl group.

In the case where Ra′³ represents a cyclic hydrocarbon group, the cyclic hydrocarbon group may be aliphatic or aromatic, and may be polycyclic or monocyclic. As the monocyclic aliphatic hydrocarbon group, a group in which 1 hydrogen atom has been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 8 carbon atoms, and specific examples thereof include cyclopentane, cyclohexane and cyclooctane. As the polycyclic group, a group in which 1 hydrogen atom has been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

In the case where the hydrocarbon group is an aromatic hydrocarbon group, examples of the aromatic ring contained in the aromatic hydrocarbon group include aromatic hydrocarbon rings, such as benzene, biphenyl, fluorene, naphthalene, anthracene and phenanthrene; and aromatic hetero rings in which part of the carbon atoms constituting the aforementioned aromatic hydrocarbon rings has been substituted with a hetero atom. Examples of the hetero atom within the aromatic hetero rings include an oxygen atom, a sulfur atom and a nitrogen atom.

Specific examples of the aromatic hydrocarbon group include a group in which 1 hydrogen atom has been removed from the aforementioned aromatic hydrocarbon ring (aryl group); and a group in which 1 hydrogen atom of the aforementioned aryl group has been substituted with an alkylene group (an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group). The alkylene group (alkyl chain within the arylalkyl group) preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1.

In the case where Ra′³ is bonded to Ra′¹ or Ra′² to form a ring, the cyclic group is preferably a 4 to 7-membered ring, and more preferably a 4 to 6-membered ring. Specific examples of the cyclic group include tetrahydropyranyl group and tetrahydrofuranyl group.

Examples of the acid dissociable group for protecting the carboxy group as a polar group include the acid dissociable group represented by general formula (a1-r-2) shown below (hereafter, with respect to the acid dissociable group represented by the following formula (a1-r-2), the acid dissociable group constituted of alkyl groups is referred to as “tertiary ester-type acid dissociable group”).

In the formula, Ra′⁴ to Ra′⁶ each independently represents a hydrocarbon group, provided that Ra′⁵ and Ra′⁶ may be mutually bonded to form a ring; and * represents a valence bond.

As the hydrocarbon group for Ra′⁴ to Ra′⁶, the same groups as those described above for Ra′³ can be mentioned. Ra′⁴ is preferably an alkyl group having from 1 to 5 carbon atoms. In the case where Ra′⁵ and Ra′⁶ are mutually bonded to form a ring, a group represented by general formula (a1-r2-1) shown below can be mentioned.

On the other hand, in the case where Ra′⁴ to Ra′⁶ are not mutually bonded and independently represent a hydrocarbon group, the group represented by general formula (a1-r2-2) shown below can be mentioned.

In the formulae, Ra′¹⁰ represents an alkyl group of 1 to 10 carbon atoms; Ra′¹¹ is a group which forms an aliphatic cyclic group together with a carbon atom having Ra′¹⁰ bonded thereto; and Ra′¹² to Ra′¹⁴ each independently represents a hydrocarbon group; and * represents a valence bond.

In the formula (a1-r2-1), as the alkyl group of 1 to 10 carbon atoms for Ra′¹⁰, the same groups as described above for the linear or branched alkyl group for Ra′³ in the formula (a1-r-1) are preferable. In the formula (a1-r2-1), as the aliphatic cyclic group which is formed by Ra′¹¹, the same groups as those described above for the cyclic alkyl group for Ra′³ in the formula (a1-r-1) are preferable.

In the formula (a1-r2-2), it is preferable that Ra′¹² and Ra′¹⁴ each independently represents an alkyl group or 1 to 10 carbon atoms, and it is more preferable that the alkyl group is the same group as the described above for the linear or branched alkyl group for Ra′³ in the formula (a1-r-1), it is still more preferable that the alkyl group is a linear alkyl group of 1 to 5 carbon atoms, and it is particularly preferable that the alkyl group is a methyl group or an ethyl group.

In the formula (a1-r2-2), it is preferable that Ra′¹³ is the same group as described above for the linear, branched or cyclic alkyl group for Ra′³ in the formula (a1-r-1). Among these, the same cyclic alkyl group as those describe above for Ra′³ is more preferable.

Specific examples of the formula (a1-r2-1) are shown below. In the formulae shown below, “*” represents a valence bond.

Specific examples of the formula (a1-r2-2) are shown below.

Examples of the acid dissociable group for protecting a hydroxy group as a polar group include the acid dissociable group represented by general formula (a1-r-3) shown below (hereafter, referred to as “tertiary alkyloxycarbonyl-type acid dissociable group”).

In the formula, Ra′⁷ to Ra′⁹ each independently represents an alkyl group; and * represents a valence bond.

In the formula (a1-r-3), Ra′⁷ to Ra′⁹ is preferably an alkyl group of 1 to 5 carbon atoms, and more preferably an alkyl group of 1 to 3 carbon atoms.

Further, the total number of carbon atoms within the alkyl group is preferably 3 to 7, more preferably 3 to 5, and most preferably 3 or 4.

Examples of the structural unit (a1) include a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid; a structural unit derived from hydroxystyrene or a hydroxystyrene derivative in which at least a part of the hydrogen atom of the hydroxy group is protected with a substituent containing an acid decomposable group; and a structural unit derived from vinylbenzoic acid or a vinylbenzoic acid derivative in which at least a part of the hydrogen atom within —C(═O)—OH is protected with a substituent containing an acid decomposable group.

As the structural unit (a1), a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is preferable.

As the structural unit (a1), structural units represented by general formula (a1-1) or (a1-2) shown below are preferable.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; Va¹ represents a divalent hydrocarbon group which may contain an ether bond, an urethane bond or an amide bond; each n_(a1) represents an integer of 0 to 2; Ra¹ represents an acid dissociable group represented by the aforementioned formula (a1-r-1) or (a1-r-2); Wa¹ represents a hydrocarbon group having a valency of n_(a2)+1; n_(a2) represents an integer of 1 to 3; and Ra² represents an acid dissociable group represented by the aforementioned formula (a1-r-1) or (a1-r-3).

In general formula (a1-1), as the alkyl group of 1 to 5 carbon atoms for R, a linear or branched alkyl group of 1 to 5 carbon atoms is preferable, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group. The halogenated alkyl group of 1 to 5 carbon atoms represented by R is a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

The hydrocarbon group for Va¹ may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity. The aliphatic hydrocarbon group as the divalent hydrocarbon group for Va¹ may be either saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given.

Further, as the group for Va¹, a group in which the aforementioned divalent hydrocarbon group has been bonded via an ether bond, urethane bond or amide bond can be mentioned.

The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 6, still more preferably 1 to 4, and most preferably 1 to 3.

As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [—CH₂—], an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃—], a tetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples include various alkylalkylene groups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂—; alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; and alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and —CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable.

As examples of the hydrocarbon group containing a ring in the structure thereof, an alicyclic hydrocarbon group (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the alicyclic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group, and a group in which the alicyclic group is interposed within the aforementioned linear or branched aliphatic hydrocarbon group, can be given. As the linear or branched aliphatic hydrocarbon group, the same groups as those described above can be used.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or a polycyclic group. As the monocyclic aliphatic hydrocarbon group, a group in which 2 hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclopentane and cyclohexane. As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The aromatic hydrocarbon group is a hydrocarbon group having an aromatic ring.

The aromatic hydrocarbon group as the divalent hydrocarbon group for Va¹ preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 10. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group.

Examples of the aromatic ring contained in the aromatic hydrocarbon group include aromatic hydrocarbon rings, such as benzene, biphenyl, fluorene, naphthalene, anthracene and phenanthrene; and aromatic hetero rings in which part of the carbon atoms constituting the aforementioned aromatic hydrocarbon rings has been substituted with a hetero atom. Examples of the hetero atom within the aromatic hetero rings include an oxygen atom, a sulfur atom and a nitrogen atom.

Specific examples of the aromatic hydrocarbon group include a group in which two hydrogen atoms have been removed from the aforementioned aromatic hydrocarbon ring (arylene group); and a group in which one hydrogen atom has been removed from the aforementioned aromatic hydrocarbon ring (aryl group) and one hydrogen atom has been substituted with an alkylene group (such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group). The alkylene group (alkyl chain within the arylalkyl group) preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1.

In the aforementioned formula (a1-2), the hydrocarbon group for Wa¹ having a valency of n_(a2)+1 may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic cyclic group refers to a hydrocarbon group that has no aromaticity, and may be either saturated or unsaturated, but is preferably saturated. Examples of the aliphatic hydrocarbon group include a linear or branched aliphatic hydrocarbon group, an aliphatic hydrocarbon group containing a ring in the structure thereof, and a combination of the linear or branched aliphatic hydrocarbon group and the aliphatic hydrocarbon group containing a ring in the structure thereof. As the specific examples thereof, the same groups as those described above for Va¹ in the aforementioned formula (a1-1) can be mentioned.

The valency of n_(a2)+1 is preferably divalent, trivalent or tetravalent, and divalent or trivalent is more preferable.

As the structural unit (a1-2), a structural unit represented by general formula (a1-2-01) shown below is particularly desirable.

In the formula (a1-2-01), Ra² represents an acid dissociable group represented by the aforementioned formula (a1-r-1) or (a1-r-3); n_(a)e is an integer of 1 to 3, preferably 1 or 2, and more preferably 1; c is an integer of 0 to 3, preferably 0 or 1, and more preferably 1; R is the same as defined above.

Specific examples of the structural units (a1-1) and (a1-2) are shown below. In the formulae shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

In the component (A), the amount of the structural unit (a1) based on the combined total of all structural units constituting the component (A) is preferably 20 to 80 mol %, more preferably 20 to 75 mol %, and still more preferably 25 to 70 mol %. By ensuring the lower limit, various lithography properties such as sensitivity, resolution and LWR are improved. On the other hand, when the amount of the structural unit (a1) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

(Structural Unit (a2))

In the present embodiment, the base component preferably contains a structural unit (a2) having an —SO₂— containing cyclic group, a lactone-containing cyclic group, a carbonate-containing cyclic group or any other heterocyclic group.

When the component (A) is used for forming a resist film, the structural unit (a2) containing an —SO₂— containing cyclic group, a lactone-containing cyclic group, a carbonate-containing cyclic group or any other heterocyclic group is effective in improving the adhesion between the resist film and the substrate.

A structural unit (a1) (described later) which contains an —SO₂— containing cyclic group, a lactone-containing cyclic group, a carbonate-containing cyclic group or any other heterocyclic group falls under the definition of the structural unit (a2); however, such a structural unit is regarded as a structural unit (a1), and does not fall under the definition of the structural unit (a2).

The structural unit (a2) is preferably a structural unit represented by general formula (a2-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms, a halogenated alkyl group of 1 to 5 carbon atoms, a hydroxyalkyl group, an alkoxy group; Ya²¹ represents a single bond or a divalent linking group; La²¹ represents —O—, —COO—, —CON(R′)—, —OCO—, —CONHCO— or —CONHCS—; and R′ represents a hydrogen atom or a methyl group, provided that, when La²¹ represents —O—, Ya²¹ does not represents —CO—; and Ra²¹ represents an —SO₂— containing cyclic group, a lactone-containing cyclic group, a carbonate-containing cyclic group or any other heterocyclic group.

In formula (a2-1), Ra²¹ represents an —SO₂— containing cyclic group, a lactone-containing cyclic group, a heterocyclic group or a carbonate-containing cyclic group.

The term “—SO₂— containing cyclic group” refers to a cyclic group which contains a ring containing —SO₂— within the ring skeleton thereof, more specifically, a cyclic group in which the sulfur atom (S) of —SO₂— forms part of the ring skeleton. The ring containing —SO₂— within the ring skeleton thereof is counted as the first ring. A cyclic group in which the only ring structure is the ring that contains —SO₂— in the ring skeleton thereof is referred to as a monocyclic group, and a group containing other ring structures is described as a polycyclic group regardless of the structure of the other rings. The —SO₂— containing cyclic group may be either a monocyclic group or a polycyclic group.

As the —SO₂— containing cyclic group, a cyclic group containing —O—SO₂— within the ring skeleton thereof, i.e., a cyclic group containing a sultone ring in which —O—S— within the —O—SO₂— group forms part of the ring skeleton thereof is particularly desirable. More specific examples of the —SO₂— containing cyclic group include groups represented by general formulas (a5-r-1) to (a5-r-4) shown below.

In the formulae, each Ra′⁵¹ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group; R″ represents a hydrogen atom or an alkyl group; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and n′ represents an integer of 0 to 2.

In general formulae (a5-r-1) to (a5-r-4), A″ is the same as defined for A″ in general formulae (a2-r-1) to (a2-r-7) described later. The alkyl group, alkoxy group, halogen atom, halogenated alkyl group, —COOR″, —OC(═O)R″ and hydroxyalkyl group for Ra′⁵′ are the same as defined for Ra′²′ in general formulae (a2-r-1) to (a2-r-7) described later.

Specific examples of the groups represented by the aforementioned general formulae (a5-r-1) to (a5-r-4) are shown below. In the formulae shown below, “Ac” represents an acetyl group.

In the present embodiment, when the structural unit (a2) contains an —SO₂— containing cyclic group, there is no particular limitation as long as the acrylate ester monomer containing an —SO₂— containing cyclic group has a log P value of less than 1.2. Among these, a group represented by the aforementioned general formula (a5-r-1) is preferable, at least one member selected from the group consisting of groups represented by the aforementioned chemical formulas (r-s1-1-1), (r-s1-1-18), (r-s1-3-1) and (r-s1-4-1) is more preferable, and a group represented by chemical formula (r-s1-1-1) is most preferable.

The term “lactone-containing cyclic group” refers to a cyclic group including a ring containing a —O—C(═O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings. The lactone-containing cyclic group may be either a monocyclic group or a polycyclic group.

As the lactone-containing cyclic group, there is no particular limitation, and an arbitrary group may be used. Specific examples include groups represented by general formulae (a2-r-1) to (a2-r-7) shown below. Hereinbelow, “*” represents a valence bond.

In the formulae, each Ra′²¹ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group; R″ represents a hydrogen atom or an alkyl group; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; n′ represents an integer of 0 to 2; and m′ represents 0 or 1.

In general formulae (a2-r-1) to (a2-r-7) above, A″ represents an oxygen atom (—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom. As the alkylene group of 1 to 5 carbon atoms for A″, a linear or branched alkylene group is preferable, and examples thereof include a methylene group, an ethylene group, an n-propylene group and an isopropylene group. Examples of alkylene groups that contain an oxygen atom or a sulfur atom include the aforementioned alkylene groups in which —O— or —S— is bonded to the terminal of the alkylene group or present between the carbon atoms of the alkylene group. Specific examples of such alkylene groups include —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂— and —CH₂—S—CH₂—. As A″, an alkylene group of 1 to 5 carbon atoms or —O— is preferable, more preferably an alkylene group of 1 to 5 carbon atoms, and most preferably a methylene group. Each Ra′²¹ independently represents an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group.

The alkyl group for Ra′²¹ is preferably an alkyl group of 1 to 5 carbon atoms.

The alkoxy group for Ra′²¹ is preferably an alkoxy group of 1 to 6 carbon atoms.

The alkoxy group is preferably a linear or branched alkoxy group. Specific examples of the alkoxy groups include the aforementioned alkyl groups for Ra′²¹ having an oxygen atom (—O—) bonded thereto.

As examples of the halogen atom for Ra′²¹, a fluorine atom, chlorine atom, bromine atom and iodine atom can be given. Among these, a fluorine atom is preferable.

Examples of the halogenated alkyl group for Ra′²¹ include groups in which part or all of the hydrogen atoms within the aforementioned alkyl group for Ra′²¹ has been substituted with the aforementioned halogen atoms. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable.

Specific examples of the groups represented by the aforementioned general formulae (a2-r-1) to (a2-r-7) are shown below.

In the present embodiment, the structural unit (a2) preferably has a group represented by the aforementioned formula (a2-r-1) or (a2-r-2), and more preferably a group represented by the aforementioned chemical formula (r-1c-1-1) or (r-1c-2-7).

The term “carbonate-containing cyclic group” refers to a cyclic group including a ring containing a —O—C(═O)—O— structure (carbonate ring). The term “carbonate ring” refers to a single ring containing a —O—C(═O)—O— structure, and this ring is counted as the first ring. A carbonate-containing cyclic group in which the only ring structure is the carbonate ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings. The carbonate-containing cyclic group may be either a monocyclic group or a polycyclic group.

Specific examples include groups represented by general formulas (ax3-r-1) to (ax3-r-3) shown below.

In the formulae, each Ra′^(x31) independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group; R″ represents a hydrogen atom or an alkyl group; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and q′ represents 0 or 1.

In general formulae (ax3-r-1) to (ax3-r-3), specific examples of A″ is the same as defined for A″ in general formulae (a2-r-1) to (a2-r-7). Examples of the alkyl group, alkoxy group, halogen atom, halogenated alkyl group, —COOR″, —OC(═O)R″ and hydroxyalkyl group for Ra′^(x31) include the same groups as those described above in the explanation of Ra′²¹ in the general formulas (a2-r-1) to (a2-r-7).

Specific examples of the groups represented by the aforementioned general formulae (ax3-r-1) to (ax3-r-3) are shown below.

A “heterocyclic group” refers to a cyclic group containing, in addition to carbon, 1 or more atoms other than carbon. Examples of the heterocyclic group include heterocyclic groups represented by the aforementioned formulae (r-hr-1) to (r-hr-16) and nitrogen-containing heterocyclic groups. Examples of the nitrogen-containing heterocyclic groups include cycloalkyl groups of 3 to 8 carbon atoms which may be substituted with 1 or 2 oxo groups. Preferable examples of the cycloalkyl group include 2,5-dioxopyrrolidine and 2,6-dioxopiperidine.

As the structural unit (a2) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

When the component (A1) contains the structural unit (a2), the amount of the structural unit (a2) based on the combined total of all structural units constituting the component (A) is preferably 1 to 80 mol %, more preferably 5 to 70 mol %, still more preferably 10 to 65 mol %, and most preferably 10 to 60 mol %. When the amount of the structural unit (a2) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a2) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units, and various lithography properties and pattern shape can be improved.

(Structural Unit (a3))

The structural unit (a3) is a structural unit containing a polar group-containing aliphatic hydrocarbon group (provided that the structural units that fall under the definition of structural units (a1) and (a2) are excluded).

When the component (A1) includes the structural unit (a3), it is presumed that the hydrophilicity of the component (A1) is enhanced, thereby contributing to improvement in resolution.

Examples of the polar group include a hydroxyl group, cyano group, carboxyl group, or hydroxyalkyl group in which part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms, although a hydroxyl group is particularly desirable.

Examples of the aliphatic hydrocarbon group include linear or branched hydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms, and cyclic aliphatic hydrocarbon groups (cyclic groups). These cyclic groups can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The cyclic group is preferably a polycyclic group, more preferably a polycyclic group of 7 to 30 carbon atoms.

Of the various possibilities, structural units derived from an acrylate ester that include an aliphatic polycyclic group that contains a hydroxyl group, cyano group, carboxyl group or a hydroxyalkyl group in which part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms are particularly desirable. Examples of the polycyclic group include groups in which two or more hydrogen atoms have been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these polycyclic groups, groups in which two or more hydrogen atoms have been removed from adamantane, norbornane or tetracyclododecane are preferred industrially.

As the structural unit (a3), there is no particular limitation as long as it is a structural unit containing a polar group-containing aliphatic hydrocarbon group, and an arbitrary structural unit may be used.

The structural unit (a3) is preferably a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group.

When the aliphatic hydrocarbon group within the polar group-containing aliphatic hydrocarbon group is a linear or branched hydrocarbon group of 1 to 10 carbon atoms, the structural unit (a3) is preferably a structural unit derived from a hydroxyethyl ester of acrylic acid. On the other hand, when the hydrocarbon group is a polycyclic group, structural units represented by formulas (a3-1), (a3-2) and (a3-3) shown below are preferable.

In the formulas, R is the same as defined above; j is an integer of 1 to 3; k is an integer of 1 to 3; t′ is an integer of 1 to 3; 1 is an integer of 1 to 5; and s is an integer of 1 to 3.

In formula (a3-1), j is preferably 1 or 2, and more preferably 1. When j is 2, it is preferable that the hydroxyl groups be bonded to the 3rd and 5th positions of the adamantyl group. When j is 1, it is preferable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

j is preferably 1, and it is particularly desirable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

In formula (a3-2), k is preferably 1. The cyano group is preferably bonded to the 5th or 6th position of the norbornyl group.

In formula (a3-3), t′ is preferably 1. l is preferably 1. s is preferably 1. Further, it is preferable that a 2-norbornyl group or 3-norbornyl group be bonded to the terminal of the carboxy group of the acrylic acid. The fluorinated alkyl alcohol is preferably bonded to the 5th or 6th position of the norbornyl group.

As the structural unit (a3) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

The amount of the structural unit (a3) within the component (A1) based on the combined total of all structural units constituting the component (A1) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, and still more preferably 5 to 25 mol %.

When the amount of the structural unit (a3) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a3) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

The component (A1) may also include a structural unit (a4) which is other than the above-mentioned structural units (a1), (a2) and (a3).

(Structural Unit (a4))

The structural unit (a4) is a structural unit containing an acid non-dissociable cyclic group. When the component (A1) includes the structural unit (a4), dry etching resistance of the resist pattern to be formed is improved. Further, the hydrophobicity of the component (A1) is further improved. Increase in the hydrophobicity contributes to improvement in terms of resolution, shape of the resist pattern and the like, particularly in an organic solvent developing process.

An “acid non-dissociable, aliphatic cyclic group” in the structural unit (a4) refers to a cyclic group which is not dissociated by the action of acid generated from the component (B) described later upon exposure, and remains in the structural unit.

As the structural unit (a4), a structural unit which contains a non-acid-dissociable aliphatic cyclic group, and is also derived from an acrylate ester is preferable. Examples of this cyclic group include the same groups as those described above in relation to the aforementioned structural unit (a1), and any of the multitude of conventional groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least one polycyclic group selected from amongst a tricyclodecyl group, adamantyl group, tetracyclododecyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms.

Specific examples of the structural unit (a4) include units with structures represented by general formulas (a4-1) to (a4-7) shown below.

In the formulae, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

As the structural unit (a4) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

When the structural unit (a4) is included in the component (A1), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the component (A1) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %.

The component (A1) is preferably a copolymer having the structural units (a1), (a2) and (a3).

The component (A1) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN) or dimethyl 2,2′-azobis(isobutyrate).

Furthermore, in the component (A1), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the component (A1). Such a copolymer having introduced a hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

In the present invention, the weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (A1) is not particularly limited, but is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and most preferably 2,000 to 20,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory.

As the component (A1), one kind of compound may be used alone, or two or more kinds of compounds may be used in combination.

In the component (A), the amount of the component (A1) based on the total weight of the component (A) is preferably 25% by weight or more, more preferably 50% by weight or more, still more preferably 75% by weight or more, and may be even 100% by weight. When the amount of the component (A1) is 25% by weight or more, various lithography properties are improved.

In the present embodiment, as the component (A), one kind of compound may be used, or two or more kinds of compounds may be used in combination.

In the present embodiment, the amount of the component (A) can be appropriately adjusted depending on the thickness of the resist film to be formed, and the like.

<Acid Generator Component; Component (B)>

In the present invention, the resist composition includes an acid generator component (B) (hereafter, referred to as “component (B)”) which generates acid upon exposure. The component (B) includes at least one acid generator (B1) represented by general formula (b1) shown below, at least one acid generator (B2) represented by general formula (b2) shown below, and at least one acid generator (B3) represented by general formula (b3) shown below.

[Chemical Formula 27]

R¹—Y¹—(CF₂)_(n)—SO₃ ⁻M₁ ⁺  (b1)

R²—(CH₂)_(m)—SO₃ ⁻M₂ ⁺  (b2)

R³—COO⁻M₃ ⁺  (b3)

In the formulae, R¹ to R³ each independently represents a cyclic group which may have a substituent, a chain alkyl group, or a chain alkenyl group; Y¹ represents a single bond or a divalent linking group containing an oxygen atom; M₁ ⁺ to M₃ ⁺ represents a monovalent organic cation; n represents an integer of 1 to 4; m represents an integer of 0 to 4; provided that, when m is 0, the carbon atom adjacent to the sulfur atom within R² has no fluorine atom bonded thereto.

[Component (B1)]

—Anion Moiety

In formula (b1), R¹ represents a cyclic group which may have a substituent, a chain alkyl group, or a chain alkenyl group.

(Cyclic Group which May have a Substituent for R¹)

The cyclic group is preferably a cyclic hydrocarbon group, and the cyclic hydrocarbon group may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group.

As the aromatic hydrocarbon group for R¹, groups in which one hydrogen atom has been removed from an aromatic hydrocarbon ring described above in relation to the divalent aromatic hydrocarbon group for Va¹ in the formula (a1-1) or an aromatic compound containing two or more aromatic ring can be mentioned, and a phenyl group or a naphthyl group is preferable.

As the cyclic aliphatic hydrocarbon group for R¹, groups in which one hydrogen atom has been removed from a monocycloalkane or a polycycloalkane exemplified above in the explanation of the divalent aliphatic hydrocarbon group for Va¹ in the formula (a1-1) can be mentioned, and an adamantyl group or a norbornyl group is preferable.

Further, the cyclic hydrocarbon group for R¹ may contain a hetero atom like as a heterocycle, and specific examples thereof include lactone-containing cyclic groups represented by the aforementioned general formulas (a2-r-1) to (a2-r-7), —SO₂— containing cyclic groups represented by the aforementioned formulas (a5-r-1) to (a5-r-4) and heterocyclic groups represented by formulae (r-hr-1) to (r-hr-16) shown below.

As the substituent for the cyclic hydrocarbon group for R¹, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carbonyl group, a nitro group or the like may be used.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the aforementioned halogenated alkyl group includes a group in which a part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

(Chain Alkyl Group which May have a Substituent for R¹)

The chain alkyl group for R¹ may be linear or branched.

The linear alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched alkyl group preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

(Chain Alkenyl Group which May have a Substituent for R¹)

The chain alkenyl group for R¹ may be linear or branched, and preferably has 2 to 10 carbon atoms, more preferably 2 to 5 carbon atoms, still more preferably 2 to 4 carbon atoms, and most preferably 3 carbon atoms. Examples of linear alkenyl groups include a vinyl group, a propenyl group (an allyl group) and a butynyl group. Examples of branched alkenyl groups include a 1-methylpropenyl group and a 2-methylpropenyl group.

Among the above-mentioned examples, as the chain alkenyl group, a propenyl group is particularly desirable.

As the substituent for the chain alkyl group or alkenyl group for R¹, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carbonyl group, a nitro group, an amino group, a cyclic group for R¹ or the like may be used.

Among these examples, as R¹, a cyclic group which may have a substituent is preferable, and a cyclic hydrocarbon group which may have a substituent is more preferable. Specifically, a phenyl group, a naphthyl group, a group in which one or more hydrogen atoms have been removed from a polycycloalkane, a lactone-containing cyclic group represented by any one of the aforementioned formula (a2-r-1) to (a2-r-7), and an —SO₂— containing cyclic group represented by any one of the aforementioned formula (a5-r-1) to (a5-r-4).

In formula (b1), Y¹ represents a single bond or a divalent linking group containing an oxygen atom.

In the case where Y¹ is a divalent linking group containing an oxygen atom, may contain an atom other than an oxygen atom. Examples of atoms other than an oxygen atom include a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom.

Examples of divalent linking groups containing an oxygen atom include non-hydrocarbon, oxygen atom-containing linking groups such as an oxygen atom (an ether bond; —O—), an ester bond (—C(═O)—O—), an oxycarbonyl group (—O—C(═O)—), an amido bond (—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond (—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon, hetero atom-containing linking groups with an alkylene group. Furthermore, the combinations may have a sulfonyl group (—SO₂—) bonded thereto. As the combination, the linking group represented by formulas (y-a1-1) to (y-a1-7) shown below can be mentioned.

In the formulae, V′¹⁰¹ represents a single bond or an alkylene group of 1 to 5 carbon atoms; V′¹⁰² represents a divalent saturated hydrocarbon group of 1 to 30 carbon atoms.

The divalent saturated hydrocarbon group for V′¹⁰² is preferably an alkylene group of 1 to 30 carbon atoms.

The alkylene group for V′¹⁰¹ and V′¹⁰² may be a linear alkylene group or a branched alkylene group, and a linear alkylene group is preferable.

Specific examples of the alkylene group for V′¹⁰¹ and V′¹⁰² include a methylene group [—CH₂—]; an alkylmethylene group, such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)— and —C(CH₂CH₃)₂—; an ethylene group [—CH₂CH₂—]; an alkylethylene group, such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂— and —CH(CH₂CH₃)CH₂—; a trimethylene group (n-propylene group) [—CH₂CH₂CH₂—]; an alkyltrimethylene group, such as —CH(CH₃)CH₂CH₂— and —CH₂CH(CH₃)CH₂—; a tetramethylene group [—CH₂CH₂CH₂CH₂—]; an alkyltetramethylene group, such as —CH(CH₃)CH₂CH₂CH₂—, —CH₂CH(CH₃)CH₂CH₂—; and a pentamethylene group [—CH₂CH₂CH₂CH₂CH₂—].

Further, part of methylene group within the alkylene group for V′¹⁰¹ and V′¹⁰² may be substituted with a divalent aliphatic cyclic group of 5 to 10 carbon atoms. The aliphatic cyclic group is preferably a divalent group in which one hydrogen atom has been removed from the cyclic aliphatic hydrocarbon group for Ra′³ in the aforementioned formula (a1-r-1), and a cyclohexylene group, 1,5-adamantylene group or 2,6-adamantylene group is preferable.

Y¹ is preferably a divalent linking group containing an ether bond or an ester bond, and groups represented by the aforementioned formulas (y-a1-1) to (y-a1-5) are preferable.

Specific examples of the anion moiety of the component (B1) include, in the case where Y¹ is a single bond, a fluorinated alkylsulfonate anion, such as a trifluoromethanesulfonate anion or a perfluorobutanesulfonate anion; and in the case where Y¹ is a divalent linking group containing an oxygen atom, an anion represented by any one of general formulae (an-1) to (an-3) shown below.

In the formulae, R″¹⁰¹ represents an aliphatic cyclic group which may have a substituent, a group represented by any one of the aforementioned formulae (r-hr-1) to (r-hr-6) or a chain-like alkyl group which may have a substituent; R″¹⁰² represents an aliphatic cyclic group which may have a substituent, a lactone-containing cyclic group represented by any one of the aforementioned general formulae (a2-r-1) to (a2-r-7) or an —SO₂— containing cyclic group represented by any one of the aforementioned general formulae (a5-r-1) to (a5-r-4); R″¹⁰³ represents an aromatic cyclic group which may have a substituent, an aliphatic cyclic group which may have a substituent or a chain-like alkenyl group which may have a substituent; V″¹⁰¹ represents a fluorinated alkylene group; L″¹⁰¹ represents —C(═O)— or —SO₂—; v″ represents an integer of 0 to 3; q″ represents an integer of 1 to 20; and n″ represents 0 or 1.

As the aliphatic cyclic group for R″¹⁰¹, R″¹⁰² and R″¹⁰³ which may have a substituent, the same groups as the cyclic aliphatic hydrocarbon group for R¹ described above are preferable. As the substituent, the same groups as those described above for substituting the cyclic aliphatic hydrocarbon group for R¹ can be mentioned.

As the aromatic cyclic group for R″¹⁰³ which may have a substituent, the same groups as the aromatic hydrocarbon group for the cyclic hydrocarbon group represented by R¹ described above are preferable. The substituent is the same as defined for the substituent for the aromatic hydrocarbon group represented by R¹.

As the chain-like alkyl group for R″¹⁰¹ which may have a substituent, the same groups as those described above for R¹ are preferable. As the chain-like alkenyl group for R″¹⁰³ which may have a substituent, the same groups as those described above for R′¹⁰¹ are preferable. V″¹⁰¹ is preferably a fluorinated alkylene group of 1 to 3 carbon atoms, and most preferably —CF₂—, —CF₂CF₂—, —CH₂CF₂—, —CF(CF₃)CF₂— or —CH(CF₃)CF₂—.

Specific examples of preferable anion moieties for the component (B1) are shown below.

—Cation Moiety

In formula (b1), M₁ ⁺ represents a monovalent organic cation.

The organic cation for M₁ ⁺ is not particularly limited. As the organic cation, sulfonium cation or an iodonium cation is preferable, and a cation represented by any one of general formulae (ca-1) to (ca-4) shown below is preferable.

In the formulae, R²⁰¹ to R²⁰⁷, R²¹¹ and R²¹² each independently represents an aryl group, an alkyl group or an alkenyl group, provided that two of R²⁰¹ to R²⁰³, R²⁰⁶ and, R²⁰⁷, or R²¹¹ and R²¹² may be mutually bonded to form a ring with the sulfur atom; R²⁰⁸ and R²⁰⁹ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; R²¹⁰ represents an aryl group which may have a substituent, an alkyl group which may have a substituent, an alkenyl group which may have a substituent or an —SO₂— containing cyclic group which may have a substituent; L²⁰¹ represents —C(═O)— or —C(═O)—O—; Y²⁰¹ each independently represents an arylene group, an alkylene group or an alkenylene group; x represents 1 or 2; and W²⁰¹ represents a linking group having a valency of (x+1). As the aryl group for R²⁰¹ to R²⁰⁷, R²¹¹ and R²¹², an unsubstituted aryl group of 6 to 20 carbon atoms can be mentioned, and a phenyl group or a naphthyl group is preferable.

The alkyl group for R²⁰¹ to R²⁰⁷, R²¹¹ and R²¹² is preferably a chain-like or cyclic alkyl group having 1 to 30 carbon atoms.

The alkenyl group for R²⁰¹ to R²⁰⁷, R²¹¹ and R²¹² preferably has 2 to 10 carbon atoms.

Specific examples of the substituent which R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² may have include an alkyl group, a halogen atom, a halogenated alkyl group, a carbonyl group, a cyano group, an amino group, an aryl group, an arylthio group and groups represented by formulae (ca-r-1) to (ca-r-7) shown below.

The aryl group within the arylthio group as the substituent is the same as defined for IV, and specific examples include a phenylthio group and a biphenylthio group.

In the formulae, R′²⁰¹ each independently represents a hydrogen atom, a cyclic group which may have a substituent, a chain-like alkyl group which may have a substituent or a chain-like alkenyl group which may have a substituent.

As the cyclic group which may have a substituent, the chain-like alkyl group which may have a substituent and the chain-like alkenyl group which may have a substituent for R′²⁰¹, the same groups as those described above for IV can be mentioned.

As the cyclic group which may have a substituent and chain-like alkyl group which may have a substituent, the same groups as those described above for the acid dissociable group represented by the aforementioned formula (a1-r-2) can be also mentioned.

When R²⁰¹ to R²⁰³, R²⁰⁶, R²⁰⁷, R²¹¹ and R²¹² are mutually bonded to form a ring with the sulfur atom, these groups may be mutually bonded via a hetero atom such as a sulfur atom, an oxygen atom or a nitrogen atom, or a functional group such as a carbonyl group, —SO—, —SO₂—, —SO₃—, —COO—, —CONH— or —N(R_(N))— (wherein R_(N) represents an alkyl group of 1 to 5 carbon atoms). The ring containing the sulfur atom in the skeleton thereof is preferably a 3 to 10-membered ring, and most preferably a 5 to 7-membered ring. Specific examples of the ring formed include a thiophene ring, a thiazole ring, a benzothiophene ring, a thianthrene ring, a benzothiophene ring, a dibenzothiophene ring, a 9H-thioxanthene ring, a thioxanthone ring, a phenoxathiin ring, a tetrahydrothiophenium ring, and a tetrahydrothiopyranium ring.

R²⁰⁸ and R²⁰⁹ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms, preferably a hydrogen atom or an alkyl group of 1 to 3 carbon atoms, and when R²⁰⁸ and R²⁰⁹ each represents an alkyl group, R²⁰⁸ and R²⁰⁹ may be mutually bonded to form a ring.

R²¹⁰ represents an aryl group which may have a substituent, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, or an —SO₂— containing cyclic group which may have a substituent.

Examples of the aryl group for R²¹⁰ include an unsubstituted aryl group of 6 to 20 carbon atoms, and a phenyl group or a naphthyl group is preferable.

As the alkyl group for R²¹⁰, a chain-like or cyclic alkyl group having 1 to 30 carbon atoms is preferable.

The alkenyl group for R²¹⁰ preferably has 2 to 10 carbon atoms.

As the —SO₂— containing cyclic group for R²¹⁰ which may have a substituent, the same “—SO₂— containing cyclic group” as those described above for Ra²¹ in the aforementioned general formula (a2-1) can be mentioned, and the group represented by the aforementioned general formula (a5-r-1) is preferable.

Each Y²⁰¹ independently represents an arylene group, an alkylene group or an alkenylene group.

Examples of the arylene group for Y²⁰¹ include groups in which one hydrogen atom has been removed from an aryl group given as an example of the aromatic hydrocarbon group for R¹ in the aforementioned formula (b1).

The alkylene group and the alkenylene group for Y²⁰¹ is the same as defined for the aliphatic hydrocarbon group as the divalent linking group represented by Va¹ in the aforementioned general formula (a1-1).

In the formula (ca-4), x represents 1 or 2.

W²⁰¹ represents a linking group having a valency of (x+1), i.e., a divalent or trivalent linking group.

As the divalent linking group for W²⁰¹, a divalent hydrocarbon group which may have a substituent is preferable, and as examples thereof, the same hydrocarbon groups as those described above for Ya²¹ in the general formula (a2-1) can be mentioned. The divalent linking group for W²⁰¹ may be linear, branched or cyclic, and cyclic is more preferable. Among these, an arylene group having two carbonyl groups, each bonded to the terminal thereof is preferable. Examples of the arylene group include a phenylene group and a naphthylene group, and a phenylene group is particularly desirable.

As the trivalent linking group for W²⁰¹, a group in which one hydrogen atom has been removed from the aforementioned divalent linking group for W²⁰¹ and a group in which the divalent linking group has been bonded to another divalent linking group can be mentioned. The trivalent linking group for W²⁰¹ is preferably a group in which 2 carbonyl groups are bonded to an arylene group.

Specific examples of preferable cations represented by formula (ca-1) include cations represented by formulae (ca-1-1) to (ca-1-65) shown below.

In the formulae, g1, g2 and g3 represent recurring numbers, wherein g1 is an integer of 1 to 5, g2 is an integer of 0 to 20, and g3 is an integer of 0 to 20.

In the formulae, R″²⁰¹ represents a hydrogen atom or a substituent, and as the substituent, the same groups as those described above for substituting R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² can be mentioned.

Specific examples of preferable cations represented by formula (ca-3) include cations represented by formulae (ca-3-1) to (ca-3-6) shown below.

Specific examples of preferable cations represented by formula (ca-4) include cations represented by formulae (ca-4-1) and (ca-4-2) shown below.

Among these examples, as the cation moiety, a cation represented by general formula (ca-1) is preferable, and a cation represented by any of formulae (ca-1-1) to (ca-1-65) is more preferable.

As the component (B1), one kind of compound may be used, or two or more kinds of compounds may be used in combination.

[Component (B2)]

—Anion Moiety

In formula (b2), R² represents a cyclic group which may have a substituent, a chain alkyl group which may have a substituent, or a chain alkenyl group which may have a substituent, and is the same as defined for R¹ in the aforementioned formula (b1).

However, when m is 0, the carbon atom adjacent to the sulfur atom within R² has no fluorine atom bonded thereto (R² is not substituted with fluorine). As a result, the anion moiety of the component (B2) becomes an appropriately weak acidic anion.

As R², an aliphatic cyclic group which may have a substituent is preferable, and a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane, tetracyclododecane or camphor (which may have a substituent) is more preferable.

The hydrocarbon group for R² may have a substituent. As the substituent, the same groups as those described above for substituting the hydrocarbon group (e.g., aromatic hydrocarbon group, aliphatic hydrocarbon group) for R³ in the formula (b3) described later may be mentioned.

Specific examples of preferable anion moieties for the component (B2) are shown below.

—Cation Moiety

In formula (b2), M₂ ⁺ represents a monovalent organic cation, and is the same as defined for M₁+ in the aforementioned formula (b1).

As the component (B2), one kind of compound may be used, or two or more kinds of compounds may be used in combination.

[Component (B3)]

—Anion Moiety

In formula (b3), R³ represents a cyclic group which may have a substituent, a chain alkyl group which may have a substituent, or a chain alkenyl group which may have a substituent, and is the same as defined for IV in the aforementioned formula (b1).

Among these, as the group for R³, an aromatic hydrocarbon group which may have a substituent, an aliphatic cyclic group which may have a substituent and a chain-like hydrocarbon group which may have a substituent are preferable. Examples of the substituent for these groups include a hydroxy group, an oxo group, an alkyl group, an aryl group, a fluorine atom, a fluorinated alkyl group, a lactone-containing cyclic group represented by any one of the aforementioned formulae (a2-r-1) to (a2-r-7), an ether bond, an ester bond, and a combination thereof. In the case where an ether bond or an ester bond is included as the substituent, the substituent may be bonded via an alkylene group, and a linking group represented by any one of the aforementioned formulae (y-a1-1) to (y-a1-5) is preferable as the substituent.

The aromatic hydrocarbon group is preferably a phenyl group or a naphthyl group.

Examples of the aliphatic cyclic group include groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

As the chain hydrocarbon group, a chain alkyl group is preferable. The chain-like alkyl group preferably has 1 to 10 carbon atoms, and specific examples thereof include a linear alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl or a decyl group, and a branched alkyl group such as a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group or a 4-methylpentyl group.

In the case where the chain-like alkyl group is a fluorinated alkyl group having a fluorine atom or a fluorinated alkyl group, the fluorinated alkyl group preferably has 1 to 11 carbon atoms, more preferably 1 to 8 carbon atoms, and still more preferably 1 to 4 carbon atoms. The fluorinated alkyl group may contain an atom other than fluorine. Examples of the atom other than fluorine include an oxygen atom, a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom.

As R³, a fluorinated alkyl group in which part or all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atom(s) is preferable, and a fluorinated alkyl group in which all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atoms (i.e., a linear perfluoroalkyl group) is more preferable.

Specific examples of preferable anion moieties for the component (B3) are shown below.

—Cation Moiety

In formula (b3), M₃ ⁺ represents a monovalent organic cation, and is the same as defined for M₁ ⁺ in the aforementioned formula (b1).

As the component (B3), one kind of compound may be used, or two or more kinds of compounds may be used in combination.

In the resist composition, the amount of the component (B), relative to 100 parts by weight of the component (A) is preferably from 0.5 to 60 parts by weight, more preferably from 1 to 50 parts by weight, and most preferably from 1 to 40 parts by weight.

When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, by virtue of the above-mentioned range, when each of the components is dissolved in an organic solvent, a homogeneous solution may be more reliably obtained and the storage stability of the resist composition becomes satisfactory.

Moreover, the component (B2) and the component (B3) exhibit a quenching effect of trapping acid generated from an acid generator or the like by ion exchange reaction.

<Photoreactive Quencher Component; Component (D)>

The resist composition of the present embodiment may further contain a photoreactive quencher component (hereafter, referred to as “component (D)”).

The component (D) functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (B) and the like upon exposure.

In the present invention, as the component (D), a nitrogen-containing organic compound is preferable.

As the component (D), an aliphatic amine, in particular, a secondary aliphatic amine or tertiary aliphatic amine is preferable.

An aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 12 carbon atoms.

Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH₃) has been substituted with an alkyl group or hydroxyalkyl group of no more than 12 carbon atoms (i.e., alkylamines or alkylalcoholamines), and cyclic amines Specific examples of alkylamines and alkylalcoholamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, and tri-n-dodecylamine; and alkyl alcohol amines such as diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, and tri-n-octanolamine. Among these, trialkylamines of 5 to 10 carbon atoms are preferable, and tri-n-pentylamine and tri-n-octylamine are particularly desirable.

Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a hetero atom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine and triethanolamine triacetate, and triethanolamine triacetate is preferable.

Further, as the component (D), an aromatic amine may be used.

Examples of aromatic amines include aniline, pyridine, 4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole and derivatives thereof, as well as diphenylamine, triphenylamine, tribenzylamine, 2,6-diisopropylaniline and N-tert-butoxycarbonylpyrrolidine.

As the component (D), one type of compound may be used alone, or two or more types may be used in combination.

The component (D) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (D) is within the above-mentioned range, the shape of the resist pattern and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer are improved.

As the component (D), one type of compound may be used, or two or more types of compounds may be used in combination.

In the present embodiment, when the resist composition contains the component (D), the amount of the component (D) relative to 100 parts by weight of the component (A) is preferably within a range from 0.1 to 15 parts by weight, more preferably from 0.3 to 12 parts by weight, and still more preferably from 0.5 to 12 parts by weight. When the amount of the component (D) is at least as large as the lower limit of the above-mentioned range, various lithography properties (such as LWR) of the resist composition are improved. Further, a resist pattern having an excellent shape can be obtained. On the other hand, when the amount of the component (D) is no more than the upper limit of the above-mentioned range, sensitivity can be maintained at a satisfactory level, and through-put becomes excellent.

<Optional Components>

[Component (E)]

In the present invention, in the resist composition, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as the component (E)) selected from the group consisting of an organic carboxylic acid, or a phosphorus oxo acid or derivative thereof can be added.

Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable.

Examples of oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esters and phenylphosphinic acid.

As the component (E), one type may be used alone, or two or more types may be used in combination.

The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

[Component (F)]

In the present invention, the resist composition of the present invention may contain a fluorine additive (hereafter, referred to as “component (F)”) for imparting water repellency to the resist film.

As the component (F), for example, a fluorine-containing polymeric compound described in Japanese Unexamined Patent Application, First Publication No. 2010-002870, Japanese Unexamined Patent Application, First Publication No. 2010-032994, Japanese Unexamined Patent Application, First Publication No. 2010-277043, Japanese Unexamined Patent Application, First Publication No. 2011-13569, and Japanese Unexamined Patent Application, First Publication No. 2011-128226 can be used.

Specific examples of the component (F) include polymers having a structural unit (f1) represented by general formula (f1-1) shown below. As the polymer, a polymer (homopolymer) consisting of a structural unit (f1) represented by formula (f1-1) shown below; a copolymer of a structural unit (f1) represented by formula (f1-1) shown below and the aforementioned structural unit (a1); and a copolymer of a structural unit (f1) represented by formula (f1-1) shown below, a structural unit derived from acrylic acid or methacrylic acid and the aforementioned structural unit (a1) are preferable. As the structural unit (a1) to be copolymerized with a structural unit (f1) represented by formula (f1-1) shown below, a structural unit derived from 1-ethyl-1-cyclooctyl(meth)acrylate or a structural unit represented by the aforementioned formula (a1-2-01) is preferable.

In the formula, R is the same as defined above; Rf¹⁰² and Rf¹⁰³ each independently represents a hydrogen atom, a halogen atom, an alkyl group of 1 to 5 carbon atoms, or a halogenated alkyl group of 1 to 5 carbon atoms, provided that Rf¹⁰² and Rf¹⁰³ may be the same or different; nf¹ represents an integer of 1 to 5; and Rf¹⁰¹ represents an organic group containing a fluorine atom.

In formula (f1-1), R is the same as defined above. As R, a hydrogen atom or a methyl group is preferable.

In formula (f1-1), examples of the halogen atom for Rf¹⁰² and Rf¹⁰³ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. Examples of the alkyl group of 1 to 5 carbon atoms for Rf¹⁰² and Rf¹⁰³ include the same alkyl group of 1 to 5 carbon atoms as those described above for R, and a methyl group or an ethyl group is preferable. Specific examples of the halogenated alkyl group of 1 to 5 carbon atoms represented by Rf¹⁰² or Rf¹⁰³ include groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. Among these, as Rf¹⁰² and Rf¹⁰³, a hydrogen atom, a fluorine atom or an alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom, a fluorine atom, a methyl group or an ethyl group is more preferable.

In formula (f1-1), nf¹ represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably 1 or 2.

In formula (f1-1), Rf¹⁰¹ represents an organic group containing a fluorine atom, and is preferably a hydrocarbon group containing a fluorine atom.

The hydrocarbon group containing a fluorine atom may be linear, branched or cyclic, and preferably has 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, and most preferably 1 to 10 carbon atoms.

It is preferable that the hydrocarbon group having a fluorine atom has 25% or more of the hydrogen atoms within the hydrocarbon group fluorinated, more preferably 50% or more, and most preferably 60% or more, as the hydrophobicity of the resist film during immersion exposure is enhanced.

Among these, as Rf¹⁰¹, a fluorinated hydrocarbon group of 1 to 5 carbon atoms is preferable, and a methyl group, —CH₂—CF₃, —CH₂—CF₂—CF₃, —CH(CF₃)₂, —CH₂—CH₂—CF₃, and —CH₂—CH₂—CF₂—CF₂—CF₂—CF₃ are most preferable.

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (F) is preferably 1,000 to 50,000, more preferably 5,000 to 40,000, and most preferably 10,000 to 30,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/Mn) of the component (F) is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.2 to 2.5.

As the component (F), one type may be used alone, or two or more types may be used in combination.

The component (F) is generally used in an amount within a range from 0.5 to 10 parts by weight, relative to 100 parts by weight of the component (A).

In the present invention, if desired, other miscible additives can also be added to the resist composition. Examples of such miscible additives include additive resins for improving the performance of the resist film, dissolution inhibitors, plasticizers, stabilizers, colorants, halation prevention agents, and dyes.

[Component (S)]

In the present invention, the resist composition can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, frequently referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and one or more kinds of any organic solvent can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist.

Examples thereof include lactones such as γ-butyrolactone; ketones such as acetone, methyl ethyl ketone (MEK), cyclohexanone, methyl-n-pentyl ketone (2-heptanone), and methyl isopentyl ketone; polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol; compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate; polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate; aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene; and dimethylsulfoxide (DMSO).

These solvents can be used individually, or in combination as a mixed solvent.

Among these, PGMEA, PGME, γ-butyrolactone and EL are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2.

Specifically, when EL or cyclohexanone is mixed as the polar solvent, the PGMEA:EL or cyclohexanone weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of at least one of PGMEA and EL with γ-butyrolactone is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5.

The amount of the component (S) is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate In general, the organic solvent is used in an amount such that the solid content of the resist composition becomes within the range from 1 to 20% by weight, and preferably from 2 to 15% by weight.

<<Method of Forming a Resist Pattern>>

In the present embodiment, a resist pattern may be formed by forming a resist film on a substrate using the aforementioned resist composition; exposing the resist film; and developing the resist film to form a resist pattern.

The method for forming a resist pattern may be performed, for example, as follows.

Firstly, the aforementioned resist composition is applied to a substrate using a spinner or the like, and a bake treatment (post applied bake (PAB)) is conducted at a temperature of 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film.

Following selective exposure of the thus formed resist film, either by exposure through a mask having a predetermined pattern formed thereon (mask pattern) using an exposure apparatus such as an ArF exposure apparatus, an electron beam lithography apparatus or an EUV exposure apparatus, or by patterning via direct irradiation with an electron beam without using a mask pattern, baking treatment (post exposure baking (PEB)) is conducted under temperature conditions of 80 to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds.

Next, the resist film is subjected to a developing treatment.

The developing treatment is conducted using an alkali developing solution in the case of an alkali developing process, and a developing solution containing an organic solvent (organic developing solution) in the case of a solvent developing process.

After the developing treatment, it is preferable to conduct a rinse treatment. The rinse treatment is preferably conducted using pure water in the case of an alkali developing process, and a rinse solution containing an organic solvent in the case of a solvent developing process.

In the case of a solvent developing process, after the developing treatment or the rinsing, the developing solution or the rinse liquid remaining on the pattern can be removed by a treatment using a supercritical fluid.

After the developing treatment or the rinse treatment, drying is conducted. If desired, bake treatment (post bake) can be conducted following the developing. In this manner, a resist pattern can be obtained.

In the present embodiment, the developing treatment may be either an alkali developing process or a solvent developing process.

(Substrate)

The substrate is not specifically limited and a conventionally known substrate can be used. For example, substrates for electronic components, and such substrates having wiring patterns formed thereon can be used. Specific examples of the material of the substrate include metals such as silicon wafer, copper, chromium, iron and aluminum; and glass. Suitable materials for the wiring pattern include copper, aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substrates provided with an inorganic and/or organic film on the surface thereof may be used. As the inorganic film, an inorganic antireflection film (inorganic BARC) can be used. As the organic film, an organic antireflection film (organic BARC) and an organic film such as a lower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is method in which at least one layer of an organic film (lower-layer organic film) and at least one layer of a resist film (upper resist film) are provided on a substrate, and a resist pattern formed on the upper resist film is used as a mask to conduct patterning of the lower-layer organic film. This method is considered as being capable of forming a pattern with a high aspect ratio. More specifically, in the multilayer resist method, a desired thickness can be ensured by the lower-layer organic film, and as a result, the thickness of the resist film can be reduced, and an extremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method in which a double-layer structure consisting of an upper-layer resist film and a lower-layer organic film is formed (double-layer resist method), and a method in which a multilayer structure having at least three layers consisting of an upper-layer resist film, a lower-layer organic film and at least one intermediate layer (thin metal film or the like) provided between the upper-layer resist film and the lower-layer organic film (triple-layer resist method).

The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiation such as ArF excimer laser, KrF excimer laser, F2 excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and soft X-rays. The resist composition of the present invention is effective to KrF excimer laser, ArF excimer laser, EB and EUV.

The exposure of the resist film can be either a general exposure (dry exposure) conducted in air or an inert gas such as nitrogen, or immersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and the lens at the lowermost point of the exposure apparatus is pre-filled with a solvent (immersion medium) that has a larger refractive index than the refractive index of air, and the exposure (immersion exposure) is conducted in this state.

The immersion medium preferably exhibits a refractive index larger than the refractive index of air but smaller than the refractive index of the resist film to be exposed. The refractive index of the immersion medium is not particularly limited as long as it satisfies the above-mentioned requirements.

Examples of this immersion medium which exhibits a refractive index that is larger than the refractive index of air but smaller than the refractive index of the resist film include water, fluorine-based inert liquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquids containing a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃, C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling point within a range from 70 to 180° C. and preferably from 80 to 160° C. A fluorine-based inert liquid having a boiling point within the above-mentioned range is advantageous in that the removal of the immersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is particularly desirable. Examples of these perfluoroalkyl compounds include perfluoroalkylether compounds and perfluoroalkylamine compounds.

Specifically, one example of a suitable perfluoroalkylether compound is perfluoro(2-butyl-tetrahydrofuran) (boiling point 102° C.), and an example of a suitable perfluoroalkylamine compound is perfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety, environment and versatility.

As an example of the alkali developing solution used in an alkali developing process, a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) can be given.

As the organic solvent contained in the organic developing solution used in a solvent developing process, any of the conventional organic solvents can be used which are capable of dissolving the component (A) (prior to exposure). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, and hydrocarbon solvents. Further, the developing solution may contain 80% or more of an organic solvent.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used.

When a surfactant is added, the amount thereof based on the total amount of the organic developing solution is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The developing treatment can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method).

The rinse treatment using a rinse liquid (washing treatment) can be conducted by a conventional rinse method. Examples of the rinse method include a method in which the rinse liquid is continuously applied to the substrate while rotating it at a constant rate (rotational coating method), a method in which the substrate is immersed in the rinse liquid for a predetermined time (dip method), and a method in which the rinse liquid is sprayed onto the surface of the substrate (spray method).

EXAMPLES

The present invention will be described more specifically with reference to the following examples, although the scope of the present invention is by no way limited by these examples.

Preparation of Resist Composition: Examples 1 to 14, Comparative Examples 1 to 6

The components shown in Tables 1 and 2 were mixed together and dissolved to obtain each resist composition.

TABLE 1 Component (B) Component Component Component Component Component Component (A) (B1) (B2) (B3) (F) (S) Example 1 (A)-1 (B1)-1 (B2)-1 (B3)-1 (F)-1 (S)-1 [100] [6.4] [4.0] [3.25] [1.5] [3600] Example 2 (A)-1 (B1)-1 (B2)-1 (B3)-1 (F)-1 (S)-1 [100] [6.4] [2.0] [3.25] [1.5] [3600] Example 3 (A)-1 (B1)-1 (B2)-2 (B3)-1 (F)-1 (S)-1 [100] [6.4] [4.2] [3.25] [1.5] [3600] Example 4 (A)-2 (B1)-1 (B2)-1 (B3)-1 (F)-1 (S)-1 [100] [6.4] [4.0] [3.25] [1.5] [3600] Example 5 (A)-1 (B1)-1 (B2)-1 (B3)-1 (F)-1 (S)-1 [100] [6.4] [4.0] [3.25] [1.5] [3600] Example 6 (A)-3 (B1)-2 (B2)-1 (B3)-2 (F)-1 (S)-1 [100] [5.8] [3.5] [3.87] [1.5] [3600] Example 7 (A)-4 (B1)-3 (B2)-3 (B3)-3 (F)-1 (S)-1 [100] [6.2] [4.2] [3.50] [1.5] [3600] Comparative (A)-1 (B1)-1 — (B3)-1 (F)-1 (S)-1 Example 1 [100] [6.4] [3.25] [1.5] [3600] Comparative (A)-1 (B1)-1 — (B3)-1 (F)-1 (S)-1 Example 2 [100] [11.6]  [3.25] [1.5] [3600] Comparative (A)-1 (B1)-1 (B2)-1 — (F)-1 (S)-1 Example 3 [100] [6.4] [4.7] [1.5] [3600]

TABLE 2 Component (B) Component Component Component Component Component Component (A) (B1) (B2) (B3) (F) (S) Example 8 (A)-5 (B1)-4 (B2)-1 (B3)-2 (F)-1 (S)-1 [100] [8.00] [4.50] [4.10] [1.5] [3600] Example 9 (A)-5 (B1)-4 (B2)-1 (B3)-2 (F)-1 (S)-1 [100] [8.00] [2.50] [4.10] [1.5] [3600] Example 10 (A)-5 (B1)-4 (B2)-2 (B3)-2 (F)-1 (S)-1 [100] [8.00] [6.00] [4.10] [1.5] [3600] Example 11 (A)-5 (B1)-4 (B2)-2 (B3)-2 (F)-1 (S)-1 [100] [8.00] [4.50] [4.10] [1.5] [3600] Example 12 (A)-5 (B1)-4 (B2)-4 (B3)-2 (F)-1 (S)-1 [100] [8.00] [4.50] [4.10] [1.5] [3600] Example 13 (A)-5 (B1)-4 (B2)-2 (B3)-1 (F)-1 (S)-1 [100] [8.00] [4.50] [3.50] [1.5] [3600] Example 14 (A)-6 (B1)-4 (B2)-2 (B3)-1 (F)-1 (S)-1 [100] [8.00] [4.50] [3.50] [1.5] [3600] Comparative (A)-5 (B1)-4 (B2)-1 — (F)-1 (S)-1 Example 4 [100] [8.00] [2.50] [1.5] [3600] Comparative (A)-5 (B1)-4 — (B3)-2 (F)-1 (S)-1 Example 5 [100] [8.00] [4.10] [1.5] [3600] Comparative (A)-5 (B1)-5 (B2)-4 — (F)-1 (S)-1 Example 6 [100] [6.00] [1.00] [1.5] [3600] (B2)-5 [5.00]

In Tables 1 and 2, the reference characters indicate the following. The values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added.

(A)-1 to (A)-6: Polymeric compounds (A)-1 to (A)-6 shown in Table 3

(B1)-1 to (B1)-5: Acid generators which are compounds represented by chemical formulae (B1)-1 to (B1)-5 shown below

(B2)-1 to (B2)-5: Acid generators which are compounds represented by chemical formulae (B2)-1 to (B2)-5 shown below

(B3)-1 to (B3)-3: Acid generators which are compounds represented by chemical formulae (B3)-1 to (B3)-3 shown below

(F)-1: fluorine-containing polymeric compound represented by chemical formula (F)-1 below.

The weight average molecular weight (Mw) and the dispersity (Mw/Mn) in terms of the polystyrene equivalent value measured by gel permeation chromatography (GPC) were 15,000 and 1.61, respectively. The composition of the copolymer (ratio (molar ratio) of the respective structural units within the structural formula) as determined by ¹³C-NMR was l/m=50/50.

(S)-1: ZX solvent (a mixed solvent of PM (propyleneglycol monomethyl ether acetate, PGMEA) and PE (propyleneglycol monomethylether, PGME) having a mixing ratio of PM:PE=7:3 (weight ratio))

TABLE 3 Polymeric Copolymer compositional ratio (ratio of compound each structural unit (molar ratio)) Mw Mw/Mn A-1 (21)/(22)/(31)/(11)/(13) = 2/2/1/3/2 8200 1.56 A-2 (21)/(22)/(31)/(11)/(13) = 2/2/1/3/2 9600 1.60 A-3 (23)/(13) = 5/5 6800 1.62 A-4 (21)/(23)/(31)/(13) = 2/2/1/5 8900 1.55 A-5 (21)/(14)/(31) = 9/7/4 7100 1.68 A-6 (21)/(24)/(14) = 4/2/4 6000 1.54

In Table 3, the reference characters of each structural unit of the copolymers indicate the following.

Formation of Solvent Development Negative-Tone Resist Pattern; Examples 1 to 7, Comparative Examples 1 to 3

An organic anti-reflection film composition (product name: ARC95, manufactured by Brewer Science Ltd.) was applied to an 12-inch silicon wafer using a spinner, and the composition was then baked at 205° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 90 nm.

Then, the resist composition in Table 1 was applied to the film using a spinner, and was then prebaked (PAB) on a hotplate at a bake temperature of 110° C. for 60 seconds and dried, thereby forming a resist film having a film thickness of 85 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser (193 nm) through a phase shift mask (PSM), using an exposure apparatus NSR-S609B (manufactured by Nikon Corporation, NA (numerical aperture)=1.30, Crosspole, immersion medium: water).

Further, a post exposure bake (PEB) was conducted at 90° C. for 60 seconds.

Next, a solvent development was conducted at 23° C. for 13 seconds using butyl acetate, followed by drying by shaking.

As a result, in each of the examples, a contact hole pattern (hereafter, referred to as “CH pattern”) in which holes having a hole diameter of 43 nm are equally spaced (pitch: 90 nm) was formed.

<Evaluation of Negative-Tone Resist Pattern>

[In-Plane Uniformity (CDU) of Pattern Size]

With respect to each CH pattern obtained above, 100 holes in the CH pattern were observed from the upper side thereof using a measuring scanning electron microscope (SEM) (product name: S-9380, manufactured by Hitachi High-Technologies Corporation; acceleration voltage: 300V), and the hole diameter (nm) of each hole was measured. From the results, the value of 3 times the standard deviation (σ) (3σ) was determined. The results are indicated “CDU” in Table 4.

The smaller the thus determined 3σ value is, the higher the level of the dimension uniformity (CD uniformity) of the holes formed in the resist film.

TABLE 4 CDU Example 1 3.98 Example 2 4.02 Example 3 3.89 Example 4 3.92 Example 5 4.09 Example 6 4.15 Example 7 4.12 Comparative 4.45 Example 1 Comparative 4.52 Example 2 Comparative 5.07 Example 3

Formation of Alkali Development Positive-Tone Resist Pattern; Examples 8 to 14, Comparative Examples 4 to 6

An organic anti-reflection film composition (product name: ARC95, manufactured by Brewer Science Ltd.) was applied to an 12-inch silicon wafer using a spinner, and the composition was then baked at 205° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 90 nm.

Then, the resist composition in Table 2 was applied to the film using a spinner, and was then prebaked (PAB) on a hotplate at a bake temperature of 110° C. for 60 seconds and dried, thereby forming a resist film having a film thickness of 90 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser (193 nm) through a phase shift mask, using an immersion exposure apparatus NSR-5609B (manufactured by Nikon Corporation, NA (numerical aperture)=1.30, Dipole, 0.78/0.97 w/o P).

Subsequently, an alkali developing treatment was conducted for 13 seconds using a 2.38% by weight tetramethylammonium hydroxide (TMAH).

Thereafter, a post exposure bake treatment was conducted at 95° C. (PEB(° C.)) for 60 seconds.

As a result, the following line and space pattern (hereafter, referred to as “LS pattern”) was formed.

LS pattern 1: 100 nm pitch/40 nm line, mask size 50 nm

[Evaluation of Line Width Roughness (LWR)]

With respect to each of the LS patterns formed in the manner as described above, the space width at 400 points in the lengthwise direction of the space were measured using a lengthwise measuring scanning electron microscope (SEM) (acceleration voltage: 300V). As the lengthwise measuring scanning electron microscope, a scanning electron microscope manufactured by Hitachi High-Technologies Corporation (product name: S-9380) was used.

From the measurement results of the space widths of each pattern, the value of 3 times the standard deviation s (i.e., 3s) was determined, and the average of the 3s values at 400 points was calculated as a yardstick of LWR. The results are indicated under “LWR” in Table 5.

The smaller the thus determined 3s value is, the lower the level of roughness of the space portion, indicating that an LS pattern having spaces with a uniform width was obtained.

TABLE 5 LWR Example 8 2.70 Example 9 2.76 Example 10 2.65 Example 11 2.65 Example 12 2.81 Example 13 2.64 Example 14 2.65 Comparative 3.02 Example 4 Comparative 3.15 Example 5 Comparative 3.67 Example 6

As seen from the results shown above, the resist patterns formed using the resist composition of the present invention containing all of the acid generator (B1), the acid generator (B2) and the acid generator (B3) exhibited excellent CDU and LWR.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

1. A resist composition comprising: a base component (A) which exhibits changed solubility in a developing solution under action of acid, and an acid-generator component (B) which generates acid upon exposure, the acid-generator component (B) comprising at least one acid generator (B1) represented by general formula (b1) shown below, at least one acid generator (B2) represented by general formula (b2) shown below, and at least one acid generator (B3) represented by general formula (b3) shown below: R¹—Y¹—(CF₂)_(n)—SO₃ ⁻M₁ ⁺  (b1) R²—(CH₂)_(m)—SO₃ ⁻M₂ ⁺  (b2) R³—COO⁻M₃ ⁺  (b3) wherein R¹ to R³ each independently represents a cyclic group which may have a substituent, a chain alkyl group, or a chain alkenyl group; Y¹ represents a single bond or a divalent linking group containing an oxygen atom; M₁ ⁺ to M₃ ⁺ each independently represents a monovalent organic cation; n represents an integer of 1 to 4; m represents an integer of 0 to 4; provided that, when m is 0, the carbon atom adjacent to the sulfur atom within R² has no fluorine atom bonded thereto.
 2. The resist composition according to claim 1, further comprising a photoreactive quencher component (D).
 3. The resist composition according to claim 1, wherein the base component (A) is a base component which exhibits increased solubility in a developing solution by the action of acid.
 4. The resist composition according to claim 1, further comprising a fluorine additive component (F) having a molecular weight of 1,000 or more.
 5. A method of forming a resist pattern, comprising: using a resist composition according to claim 1 to form a resist film on a substrate, exposing the resist film, and alkali developing the resist film to form a resist pattern.
 6. A method of forming a resist pattern, comprising: using a resist composition according to claim 1 to form a resist film on a substrate, exposing the resist film, and developing the resist film using a developing solution containing 80% or more of an organic solvent to form a resist pattern.
 7. The resist composition according to claim 1, wherein the at least one acid generator (B1) has an anion moiety represented by any one of general formulae (an-1) to (an-3) shown below:

wherein R″¹⁰¹ represents an aliphatic cyclic group which may have a substituent, a group represented by any one of formulae (r-hr-1) to (r-hr-6) shown below or a chain-like alkyl group which may have a substituent; R″¹⁰² represents an aliphatic cyclic group which may have a substituent, a lactone-containing cyclic group represented by any one of general formulae (a2-r-1) to (a2-r-7) shown below or an —SO₂— containing cyclic group represented by any one of general formulae (a5-r-1) to (a5-r-4) shown below; R″¹⁰³ represents an aromatic cyclic group which may have a substituent, an aliphatic cyclic group which may have a substituent or a chain-like alkenyl group which may have a substituent; V″¹⁰¹ represents a fluorinated alkylene group; L″¹⁰¹ represents —C(═O)— or —SO₂—; v″ represents an integer of 0 to 3; q″ represents an integer of 1 to 20; and n″ represents 0 or 1:

wherein each Ra′²¹ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group; R″ represents a hydrogen atom or an alkyl group; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; n′ represents an integer of 0 to 2; and m′ represents 0 or 1;

wherein each Ra′⁵¹ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group; R″ represents a hydrogen atom or an alkyl group; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and n′ represents an integer of 0 to
 2. 8. The resist composition according to claim 1, wherein, in general formula (b2), R² represents an aliphatic cyclic group which may have a substituent, and the aliphatic cyclic group is a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane, tetracyclododecane or camphor.
 9. The resist composition according to claim 7, wherein, in general formula (b2), R² represents an aliphatic cyclic group which may have a substituent, and the aliphatic cyclic group is a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane, tetracyclododecane or camphor.
 10. The resist composition according to claim 1, wherein, in general formula (b3), R³ represents an aromatic hydrocarbon group which may have a substituent, an aliphatic cyclic group which may have a substituent and a chain hydrocarbon group which may have a substituent, the aromatic hydrocarbon group is a phenyl group or a naphthyl group, the aliphatic cyclic group is a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane, and the chain hydrocarbon group is a chain alkyl group having 1 to 10 carbon atoms.
 11. The resist composition according to claim 7, wherein, in general formula (b3), R³ represents an aromatic hydrocarbon group which may have a substituent, an aliphatic cyclic group which may have a substituent and a chain hydrocarbon group which may have a substituent, the aromatic hydrocarbon group is a phenyl group or a naphthyl group, the aliphatic cyclic group is a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane, and the chain hydrocarbon group is a chain alkyl group having 1 to 10 carbon atoms.
 12. The resist composition according to claim 9, wherein, in general formula (b3), R³ represents an aromatic hydrocarbon group which may have a substituent, an aliphatic cyclic group which may have a substituent and a chain hydrocarbon group which may have a substituent, the aromatic hydrocarbon group is a phenyl group or a naphthyl group, the aliphatic cyclic group is a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane, and the chain hydrocarbon group is a chain alkyl group having 1 to 10 carbon atoms. 